1. Field of the Invention
The present invention relates to interfacing of application programs to physical devices (peripherals), particularly but not exclusively in the context of receiver/decoders for digital television systems.
2. Description of Related Art
The advent of digital transmission systems has opened up the possibility of using such systems for other purposes. One of these is to provide interactivity with the end user. As used herein, the term “digital transmission system” includes any transmission system for transmitting or broadcasting for example primarily audiovisual or multimedia digital data. Whilst the present invention is particularly applicable to a broadcast digital television system, the invention may also be applicable to a fixed telecommunications network for multimedia internet applications, to a closed circuit television, and so on. As used herein, the term “digital television system” includes for example any satellite, terrestrial, cable and other system.
The present invention finds specific application in a broadcast digital television system in which received signals are passed through a receiver to a receiver/decoder and thence to a television set. The term “receiver/decoder” used herein may connote a receiver for receiving either encoded or non-encoded signals, for example, television and/or radio signals, which may be broadcast or transmitted by some other means. The term may also connote a decoder for decoding received signals. Embodiments of such receiver/decoders may include a decoder integral with the receiver for decoding the received signals, for example, in a “set-top box”, such a decoder functioning, in combination with a physically separate receiver, or such a decoder including additional functions, such as a web browser, a video recorder, or a television.
The receiver/decoder decodes a compressed MPEG-type signal into a television signal for the television set. It is controlled by a remote controller handset, through an interface in the receiver/decoder, also known as a set-top box or STB. The term MPEG refers to the data transmission standards developed by the International Standards Organisation working group “Motion Pictures Expert Group” and in particular but not exclusively the MPEG-2 standard developed for digital television applications and set out in the documents ISO 13818-1, ISO 13818-2, ISO 13818-3 and ISO 13818-4. In the context of the present patent application, the term includes all variants, modifications or developments of MPEG formats applicable to the field of digital data transmission.
One way of providing the interactivity described above is to run an application on the receiver/decoder through which the television signal is received. It is desirable to enable a variety of applications to communicate with a variety of physical devices in a transparent manner. Our co-pending applications PCT/EP97/02115 and PCT/EP97/02116 describe systems in which one or more applications can be downloaded by a receiver/decoder and communicate with physical devices in the receiver/decoder such as parallel and serial interfaces and smartcard readers by means of a driver for each device and an overall device manager. As used herein, the term “smartcard” includes, but not exclusively so, any chip-based card device, or object of similar function and performance, possessing, for example, microprocessor and/or memory storage. Included in this term are devices having alternative physical forms to a card, for example key-shaped devices such as are often used in TV decoder systems.